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Uplink Open Loop Power Control for LTE HetNet Measurement and Analysis of Weather Phenomena with K-Band Rain Radar Amir Haider, Seong-Hee Lee and Seung-Hoon Hwang Dae Ik Kim and Jee Hyeon Na Division of Electrical and Electronics Engineering Electronics and Telecommunications Research Institute Dongguk University Daejeon, Korea Jun-Hyeong Park Ki-Bok Kong Park Seoul, Korea
[email protected] andSeong-Ook
[email protected] Dept. of Electrical Engineering team Dept. of Electrical Engineering
[email protected],
[email protected] Development and KAIST Kukdong Telecom KAIST
[email protected] DaeJeon, Republic of Korea Nonsan, Republic of Korea DaeJeon, Republic of Korea
[email protected] [email protected] [email protected] Abstract— In LTE cellular network, the uplink power control network (HetNet) deployment in the hotspots, the traffic from (PC) mechanism consists of two parts, an open loop (OL) PC and macro-layer can be offloaded which provides additional a closed loop (CL) PC. The OLPC determines the initial settings resources to the network. To explore the opportunities offered of the network while the CLPC settings to ordinary correct theweather errors by is essential analyze the impact of macro(Rx) and Abstract—To overcome blind spots aim of an wallHetNet, exists itbetween the to transmitter (Tx) and receiver in the OLPC In most cellular networks, OLPC radar which configurations. scans horizontally at aof high altitude, a weather small cell to OLPC parameter’s variation on the performance of antennas improve isolation between them. With these is adopted its implementation simplicity and low radar whichbecause operates of vertically, so called an atmospheric profiler, network. prime focus of thisTx paper is to mathematically methods, The leakage power between and Rx could be reduced. operation In paper, this work, we investigate effectsrainfall of the is needed. cost. In this a K-band radar for the observing analyze the OLPC parameter’s variation both macro and Fig. 1 shows manufactured antennas and theinseparation wall. OLPC parameters for macro and small cells in a heterogeneous vertically is introduced, and measurement results of rainfall are small cells by considering a HetNet environment. network A mathematical analysis is shown and(HetNet) discussed.environment. For better performance of the atmospheric B. Design of Tranceiver employed to compute a transmit power at the mobile a profiler, the radar which has high resolution even station, with low ETWORK of MODEL GG received power at the eNodeB, interferences in the network, and Fig. 2 shows a II. blockNdiagram the K-band rain radar. transmitted power is designed. With this radar, a melting layer is adetected received interference noise ratioof(SINR). To Reference signals for all PLLs in the system and clock signals andsignal some to results that showplus characteristics the meting achieve best performance, it would be the appropriate choice for every digital chip in baseband are generated by four layer arethe measured well. of α=1 and P0 =-100dBm in the small cells, and α=0.8 and P0 =frequency synthesizers. In the Tx baseband module, a field 100dBm in macro cell. FMCW; rain radar; low transmitted Keywords—K-band; programmable gate array (FPGA) controls a direct digital power; high resolution; rainfall; melting layer synthesizer (DDS) to generate an FMCW signal which Keywords—Heterogeneous Network, Uplink, Open Loop decreases with time (down-chirp) and has a center frequency Power Control, Interference, LTE. of 670 MHz. The sweep bandwidth is 50 MHz which gives the I. INTRODUCTION high range resolution of 3 m. Considering the cost, 2.4 GHz A weather radar measures meteorological I. usually INTRODUCTION signal used as a reference clock input of the DDS is split and conditions of over a wide area at a high altitude. Because it used for a local oscillator (LO). the FMCW signal is Uplink power control (PC) plays a key role in the observes weather phenomena in the area, it is mainly used for transmitted toward raindrops with the power of only 100 mW. performance of cellular networks. There are mainly two weather forecasting. However, blind spots exist because an Beat frequency which has data of the range and the radial methods the power LTE PC; an which open loop power ordinary for weather radarcontrol scans inhorizontally, results in velocity of raindrops is carried by 60 MHz and applied to the control (OL)inPC and a closed loop power controlat(CL) PC and [1]. difficulties obtaining information on rainfall higher input ofFluid the Rx baseband module. Inbetween the Rxneighboring basebandsmall module, Figure 1. model for HetNet; separation cell’s The purpose of PC is to provide the starting point to set the lower altitudes than the specific altitude. Therefore, a weather is 2R. quadrature demodulationeNodeBs is performed by a digital down user equipment (UE) uplink transmit power, in order to radar that covers the blind spots is required. converter (DDC). Thus, detectable range can be doubled than accomplish the necessary network quality. The power control usual. Two Dimensional-Fast Fourier Transform (2D-FFT) is A weather radar that scans vertically could solve the settings compensate for interference offered from a UE to performed by two FPGAs. Because the 2D FFT is performed problem. kind of weatherresulting radar, soincalled an atmospheric other usersThis of same network, improved battery life with 1024 beat signals, the radar can have high resolution of profiler, points towards theinitiated sky and atobserves of the UE. Uplink PC is the UEmeteorological based on the the radial velocity. Finally, data of raindrops are transferred to conditions according to the height [1]. Also, because the information in the downlink configurations, transmitted by a PC with local LAN via the an UDP protocol. TABLE I. atmospheric profiler operates continuously a fixed eNodeB. OLPC playsusually the role in compensation foratthe path shows main specification of the system. position, it could catchchannel the sudden change of shadowing weather in and the loss as well as other variations like specificOn area. noise. the other hand, the CLPC tends to improve the OLPC configuration by mitigating the fasthas fading introduced In this paper, K-band rain radar which low transmitted by the channel. CLPC employs transmit power control (TPC) power and high resolutions of the range and the velocity is commands for further adjustments in the transmitted power of introduced. The frequency modulated continuous wave the UE [2].technique G (FMCW) is used to achieve high sensitivity and
reduce thedeploying cost of the system. In addition, meteorological While networks in areas having high density of resultssuch are as discussed. Reflectivity, a fallareas, speedthe of increased raindrops UEs urban and metropolitan and Doppler spectrum measured when it rained are described, traffic demands should be taken into account while and characteristics of the melting layer are as well. configuring the network parameters [3].analyzed Areas with such traffic demands are termed as hotspots in the LTE network. To meetII.theDEVELOPMENT high traffic demands and R toAIN provide reliable quality OF K-BAND RADAR SYSTEM of service to the users, small cells are deployed in the hotspots. To address the issues like network coverage, service quality A. Antenna andTo capacity, small cell deployment the planned macrogain, cell suppress side-lobe levels and in increase an antenna is provided as a promising solution [4]. With heterogeneous offset dual reflector antennas are used [2]. Also, separation
Figure 2. Fluid model integral limits for calculation of interference.
A heterogeneous LTE network is considered in this paper and focus is on the uplink only. Uniform distribution of small cells is assumed inside one macro cell. Fluid model [5] is employed for the analytical analysis of the network, as shown in Fig.1. AtFig.the omni-directional antennas are modeled to 1. eNodeB, Manufactured antenna and separation wall. provide network coverage in each cell. Rnt=1000m and
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R=200m denote the network range that is macro cell radius and small cell radius, respectively. Uniform distribution of UEs is assumed in both macro and small cell areas in this analysis [6].
So the total interference in the HetNet environment can be given as: (8)
A. Transmit and receive power For the above described network model, the uplink transmit power PTx is given as: PTx = Po+ α.PL
[dBm]
C. Received SINR formulation The received signal to interference and noise ratio (SINR) for user u can be obtained by dividing eq. (5) by eq. (8) as:
(2) (9)
And the received power PRx at the eNodeB is: PRx= P0+ α.PL-PL= P0+ (α-1) PL
[dBm]
The impact of noise and shadowing is not considered in this analysis. Variation is expected in the results if the impact of shadowing and noise is also included [7].
(3)
Free space model is employed for pathloss estimation depending upon the distance of UE from the eNodeB. The mathematical expression for the free space model is given as: PL=32.45 + 20log10 (dm) +20log10 (fMHz)
III.
PERFORMANCE EVALUATION
In HetNet environment, most of the traffic load is carried out by the small cells while the macro cell provides the back bone network support. So, in order to see the impact of OLPC parameter’s variation in HetNet, the network performance is analyzed with same parameters for both macro and small cells. Fig.3 shows the impact of identical OLPC parameters on the received SINR in this case. The target is to transmit at lowest possible power while maintaining the necessary network requirements for all the users. α=1 and P0G =-100dBm in small cells result in the lowest transmit power while there is room to reduce the transmit power in macro cell by employing lower α value. The purpose of macro cell in HetNet is to provide back end support for the small cells so, it is not favorable to have large macro cell interference in the network. The Macro cell interference results in reduced SINR for HetNet.
(4)
where, dm is the distance of UE from eNodeB in meters and fMHz is the operating frequency. B. Interference calculation Let us consider a UE u scheduled by the central small cell eNodeB b. As frequency reuse 1 is assumed, the user u suffers external interference due to only one UE per PRB from each of the network’s small cells. From eq. (2), the received power at the eNodeB b from UE u can be written as: (5) where, P0 = 10log (p0) (P0 in dBm and p0 in mW) is the target received power and plu,b is the pathloss between the UE u and eNodeB b. In Fig.1, the central small cell has radius R and is surrounded by two interfering rings of small cells at distance 2nR (n=1, 2). The network size is the radius of the Macro cell given as Rnt=5R. Being a key assumption of fluid model, the external interference in central small cell can be modeled by substituting equivalent density ρue for interfering transmitters instead of a fixed finite number. By considering a UE v scheduled by another eNodeB c which is on same PRB as UE u, the external interference offered to UE u in the central small cell can be estimated. The detailed description is depicted in Fig.2. By this approach, the small cell interference expression is approximated as: (6) Where, v(b) designates UE scheduled by eNodeB b. As there is only one macro cell under consideration, so the macro cell interference can be formulated as:
Figure 3. Received SINR in HetNet with identical OLPC parameters in macro and small cells
(7)
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In the second step, received SINR for the HetNet is analyzed by adopting α=0.8 for macro cell instead of 1. From eq. (9), the received SINR of a user is shown in Fig.4. The variation in OPLC parameters for both macro and small cells is done for computing the SINR. It is clear from the Fig.4 that for lower value of α in macro cell, the received SINR is much higher as compared to same α value for both macro and small cells. For the small cell in HetNet environment, the open loop parameter, α=1 and P0G =-100dBm, ensure uniform received SINR for all the users while the macro cell at α=0.8 and P0G=100dBm ensures the back end support with no significant contribution towards interference in the network. For all other values of α and P0, in small cells, the users near the eNodeB have better received SINR but the cell edge users suffer from worst network coverage and quality, leading to outage. Hence, there is always a tradeoff for service quality between the cell average and cell edge users if we go for any other value of α and P0.
IV.
CONCLUSION
In this paper, OLPC for LTE uplink for HetNet environment is presented by adopting an analytical approach to compute the power transmitted at the mobile station, received power at the eNodeB, interference in the network and the received SINR. We show in particular that to achieve best network performance, α=1 and P0 =-100dBm, in the small cells and α=0.8 and P0 =-100dBm, in macro cell is the appropriate choice. However, if the network is interference limited, the operator can choose lower α and higher P0 value in the small cell to optimize the system performance but at the cost of reduced service quality for cell edge users. ACKNOWLEDGMENT This work was supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government (MSIP) (No.R0101-15-244, Development of 5G Mobile Communication Technologies for Hyper-connected smart services).
From the above analysis it can be inferred that for an optimum OLPC operating point, lower value of α should be employed in the macro cell to limit the interference from macro cell to the small cells while similar value of P0 can be considered for both macro and small cells. In case if the network is interference limited, lower value of α with higher P0 is admissible in the small cell but at the cost of reduced service quality for cell edge users.
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Fig.4: Received SINR in HetNet with variation in pathloss compensation factor α and P0
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3GPP “E-UTRA Physical layer procedures”, TS 36.213 V8.1.0 B. Muhammad, "Closed loop power control for LTE uplink," Master’s Thesis, Blekinge Institute of Technology, 2008. J. Li, "Uplink power control for heterogeneous networks," in Wireless Communications and Networking Conference (WCNC), 2013 IEEE, 2013, pp. 773-777. Amir Haider, Lee, Sung-Hee Lee, Dae Ik Kim, Hye Kyung Jwa, Seung Hoon Hwang”On uplink power control for small cell in LTE”KICS Winter Conference, Jan 2016. J.-M. Kelif, et al., "A fluid model for performance analysis in cellular networks," EURASIP Journal on Wireless Communications and Networking, vol. 2010, pp. 1-8. M. Coupechoux and J.-M. Kelif, "How to set the fractional power control compensation factor in LTE?," in Sarnoff Symposium, 2011 34th IEEE, 2011, pp. 1-5. J.-M. Kelif and M. Coupechoux, "Impact of topology and shadowing on the outage probability of cellular networks," in Communications, 2009. ICC'09. IEEE International Conference on, 2009, pp. 1-6.
